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Legal Studies统计具有相同年龄的学生的频率的 MySQL 查询？
您可以为此使用 COUNT(*) 和 GROUP BY。首先让我们创建一个表 −
mysql> create table DemoTable ( StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, StudentAge int ); Query OK, 0 rows affected (0.59 sec)
使用 insert 命令在表中插入记录 −
mysql> insert into DemoTable(StudentAge) values(16); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable(StudentAge) values(17); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable(StudentAge) values(18); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable(StudentAge) values(17); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable(StudentAge) values(17); Query OK, 1 row affected (0.23 sec) mysql> insert into DemoTable(StudentAge) values(17); Query OK, 1 row affected (0.08 sec) mysql> insert into DemoTable(StudentAge) values(18); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable(StudentAge) values(18); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable(StudentAge) values(19); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable(StudentAge) values(19); Query OK, 1 row affected (0.07 sec) mysql> insert into DemoTable(StudentAge) values(16); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable(StudentAge) values(16); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable(StudentAge) values(15); Query OK, 1 row affected (0.16 sec)
使用 select 语句显示表中的所有记录 −
mysql> select * from DemoTable;
这会产生以下输出 −
+-----------+------------+ | StudentId | StudentAge | +-----------+------------+ | 1 | 16 | | 2 | 17 | | 3 | 18 | | 4 | 17 | | 5 | 17 | | 6 | 17 | | 7 | 18 | | 8 | 18 | | 9 | 19 | | 10 | 19 | | 11 | 16 | | 12 | 16 | | 13 | 15 | +-----------+------------+ 13 rows in set (0.00 sec)
以下是计数频率的查询 −
mysql> select StudentAge,count(*) AS `AgeFrequency` from DemoTable group by StudentAge;
这会产生以下输出 −
+------------+--------------+ | StudentAge | AgeFrequency | +------------+--------------+ | 16 | 3 | | 17 | 4 | | 18 | 3 | | 19 | 2 | | 15 | 1 | +------------+--------------+ 5 rows in set (0.05 sec)
更新于： 30-Jul-2019
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